Frozen Evaporator Coil

The outdoor temperature never reaches the coil. What reaches it is the air in your ducts and the refrigerant inside the tubing. If the refrigerant is too cold, from low airflow or low charge, moisture on the fins freezes regardless of what the patio thermometer says.

It is usually the leading edge of the same problem, and it is a clue. Ice that begins on the small line outside the air handler and works inward tends to point at low refrigerant. Ice concentrated inside the cabinet with a filthy filter points at airflow. Note where you saw it and tell the technician.

If the filter was the cause, yes, and that is the best outcome on this page. If ice returns within a day or two with a fresh filter and open registers, the filter was a contributor, not the cause, and the system needs a proper diagnosis before it runs much longer.

If this is the first freeze and the filter was visibly loaded, run it and watch. If it has frozen before, if the filter was clean, or if you have any reason to suspect a leak, yes. A coil that freezes on a clean filter has a problem that does not go away on its own.

Possibly the compressor, if it ran for hours against solid ice or if this was one freeze among many. A technician can check the compressor's electrical draw and refrigerant temperatures for signs of liquid return. On a single freeze caught early, damage is unlikely. Repeated freezes are a different story.

Cooler nighttime return air and longer, lower-load cycles push the coil temperature closer to freezing, so a system that is marginal on airflow or charge during the day can tip over after dark. It is still the same three causes, and it still needs the same diagnosis.

Almost never on its own. Most freezes are airflow, which is cheap to fix. The exceptions are a leaking evaporator coil on an old system, or a compressor that has been damaged by repeated liquid return. In those cases we will lay out repair and replacement side by side and let the numbers speak.